Optical filters play important roles in communication systems. In particular, a narrowband flat-top reflection filter, which reflects a particular wavelength channel while letting other channels pass through, is needed to achieve the wavelength sensitivity in wavelength-division multiplexing systems. See D. K. Jacob, S. C. Dunn, and M. G. Moharam, Appl. Opt. 41, 1241 (2002). On the other hand, an all-pass transmission filter, which generates significant delay at resonance, while maintaining 100% transmission both on and off resonance, is useful for applications such as optical delay or dispersion compensation. See C. K. Madsen, J. A. Walker, J. E. Ford, K. W. Goossen, T. N. Nielsen, and G. Lenz, IEEE Photon. Technol. Lett. 12, 651 (2000). See G. Lenz and C. K. Madsen, J. Lightwave Technol. 17, 1248 (1999); and C. K. Madsen, J. A. Walker, J. E. Ford, K. W. Goossen, T. N. Nielsen, and G. Lenz, IEEE Photonics Technol. Lett. 12, 651 (2000).